Titration is an analytical chemistry technique used to determine the concentration of unknown sample solutions using solutions of known concentration. In the titration technique, the solution of known concentration is known as the titrant which is filled in the burette and the solution of unknown concentration is known as the analyte which is poured into a conical flask.
Endpoint and equivalence point are two different important stages that occur in the titration process. Numerous students mistakenly believe that the equivalence point and the endpoint of the titration are the same, although they are not. The endpoint is the moment at which an indicator changes the color of the solution. More often than not, the color change takes place after the equivalence point has been reached.
Define equivalence point in titration:
“It is a point in a titration, at which amount of titrant added is just sufficient to neutralize the analyte solution completely”
Equivalence point in titration?
The equivalence point of a chemical reaction is the point at which the number of moles of substance contained in the sample is stoichiometrically equal to the amount of titrant added. The minimum amount of titrant is required to completely neutralize or react with the analyte. In the titration of a diprotic acid, there exist many equivalence points that are multiples of the initial equivalence point.
It is also known as the stoichiometric point since it is the point at which moles of acids equal the amount of base needed to neutralize them. The equivalence point comes either closer to an endpoint or before an endpoint. This gives the point where the reaction ends.
Note that this does not mean that the ratio of acids and bases is equal to 1:1. The ratio is determined by the acid-base chemical equation in its balanced form. This does not necessarily mean that the acid-base ratio is 1:1. The ratio is calculated by the chemically balanced acid-base equation. The ratio is estimated by the balanced acid-base chemical equation.
Example of equivalence point:
Consider the sodium hydroxide (NaOH) and hydrochloric acid (HCl) titration as an example of an acid-base reaction. One mole of NaOH and one mole of HCl react chemically to form salt and water.
HCl + NaOH → NaCl + H2O
During titration, a prepared solution of NaOH is added gradually to a sample solution containing HCl and an appropriate indicator. The sodium hydroxide begins to react with the hydrochloric acid of the sample. When enough sodium hydroxide has been added to the sample to react with all of the hydrochloric acid, the equivalence point has been reached.
Methods of determining the equivalence point:
There is a different method that used to determine the equivalence point is as follows.
- Color change
- pH indicator
- Precipitation
- Conductance
- Isothermal colorimetry
- Thermometric titrimetry
- Spectroscopy
What is half equivalence point?
The halfway between the equivalence point and the starting point in a titration is known as the half equivalence point. In an acid-base titration, the half-equivalence point is where the concentration of an added base equals half of the initial acid concentration. The half-equivalence point is also known as the midpoint of titration. The half equivalence point is fairly simple to determine as the pKa of the acid is equal to the pH of the solution at this point.
Why do diprotic acids have two equivalence points?
This is due to the two ionizing hydrogen’s in the acid do not dissociate from the acid at the same time. Protons are usually donated in steps by diprotic acids. As a result, the acid will have two acid dissociation constants, the second of which will be lower than the first.
What species are present at the equivalence point?
Only neutral ions (the cation from the strong base and the anion from the strong acid) and water are present in the solution at the equivalence point. Salt and water are present at the point of equivalence in acid-base titrations.
Frequently Asked Question (FAQ):
Why is the point in the titration when neutralization occurs called the equivalence point?
Because this is the point in a titration where the relative amounts of each component in the chemical reaction are precisely defined by the coefficients in the balanced chemical equation, it's called the equivalence point.
Is the equivalence point always 7?
In a strong acid-strong base titration, the equivalence point always occurs at pH=7. It is greater than 7 for a weak acid-strong base, and less than 7 for a strong acid-weak base because only the conjugate acid is present and it’s around about 7 for the weak acid-weak base.
Why is the pH at the equivalence point not always equal to 7 in a neutralization titration? When would it be 7?
Titration is a process in which an acid and a base react to neutralize each other. However, not all of the salts that formed are neutral. When a strong acid with a weak base, will give is a slightly acidic salt, likewise, a weak acid with a strong base gives a slightly basic salt.
Consider the reaction of acetic acid (acetic acid), a weak acid, with a strong base, such as sodium hydroxide (NaOH).
A salt, sodium acetate (C2H3NaO2), and water (H2O) are generated during the neutralization reaction. As a base, the acetate ion reacts with water to produce CH3COOH and OH- CH3COO- + H2O → CH3COOH + OH- The reaction of the acetate ion raises the pH of the solution from 7-8. The pH of the solution is increases from 7.0 by this acetate ion reaction. Because the conjugate base of a strong acid is strong and weak to dissociate water, the pH for strong acid strong base titrations is 7.
People also ask:
What is equivalence point in equilibrium?
Why is it called the equivalence point?
How do you know when an equivalence point is reached?
Why isnt the pH at the equivalence point always equal to 7?
What is the pH at the first equivalence point?
How do you find pH from equivalence point?
pH at equivalence point weak acid-strong base
References:
- Wikipedia contributors. "Equivalence point." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 10 Dec. 2021.
- Vogel, A.I.; J. Mendham (2000). Vogel's Textbook of Quantitative Chemical Analysis (6th ed.).
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